1. Field of the Invention
The present invention relates to air conditioning and heating systems. More particularly, the present invention relates to air conditioning and heating systems in which a blower is used to circulate air within a building.
2. Description of Related Art Air conditioning systems typically include an air-handler that provides conditioned air to a comfort zone, such as a room or a designated area within a building. The conditioning of the air may include, but not be limited to heating, cooling, humidifying, dehumidifying, filtering, ventilating, and their various combinations. Air-handlers can also assume a variety of configurations to best serve their intended purpose.
One basic air-handler, for example, may simply include a furnace for providing heat to the comfort zone. Other residential air-handlers, known as split systems, may include separate indoor and outdoor units, with each unit having its own heat exchanger and blower. Split systems usually provide cooling and/or heating. Other systems, such as packaged or self-contained units (e.g., conventional window-mounted air conditioners) and larger, commercial air-handlers may also provide cooling and/or heating, but combine the indoor and outdoor units within a single enclosure.
Air-handlers typically include, or are associated with, one or more fans or blowers that move the air through a network of supply and return air ducts. Supply air ducts deliver the conditioned air to the rooms. Return air ducts convey the used or return air back to the air-handler for reconditioning before the supply air ducts convey the air back to the rooms.
To help keep an air-handling system clean, an air filter is usually placed in the return air duct to remove dirt and dust from the air. Such filters are often disposable cardboard or paper-type filters that are discarded when dirty.
In many cases, an electronic air cleaner is installed in the return air duct to clean the air more thoroughly. An electronic air cleaner electrostatically charges dust and other small particles in the air that passes through the cleaner. An oppositely charged collection plate in the cleaner then attracts the particles and removes them from the air stream. In order for an electronic air cleaner to be effective, air must pass through it. Thus, when an air-handler's supply air blower turns off upon satisfying the comfort zone's demand for conditioned air, the air cleaner's operation also stops. Alternatively, the blower could be kept running at its normal speed; however, that would be quite wasteful of electrical energy, as the rate of airflow for heating or cooling the air is generally much greater than that what is needed to just clean the air.
Another option would be to keep the blower running, but at a reduced speed. This could be done by simply using an inverter-driven AC induction motor to power the blower, as disclosed in U.S. Pat. No. 5,078,318. However, the cost of AC inverters increases dramatically with its current carrying capacity. Moreover, the power to operate a blower increases generally with the cube of its delivered airflow rate. Thus, the current draw of the blower motor also increases exponentially with motor speed. As a result, providing an expensive, full-sized inverter to power a blower motor at its rated speed is impractical when the inverter is only needed for providing perhaps half that speed for a current draw conceivably as low as one-eighth of the motor's rated full load current.
Still further, whereas older heating and air conditioning systems often employ a single speed indoor blower operating in conjunction with an air conditioner and/or furnace operating on a simple on-off, single-stage basis, certain newer air conditioners and furnaces employ multispeed compressors (in the case of air conditioners) and staged burners (in the case of furnaces) which are capable of operating at less than full capacity so as to save energy when outdoor conditions permit.
Thus, additional energy and cost savings can potentially be achieved by controlling the speed of the indoor blower motor in accordance with the actual demand for airflow circulation within the building rather than on a simple on-off basis.
The need therefore exists for apparatus and a methodology, in new and retrofit HVAC applications, for operating an indoor blower associated with a heating and/or air conditioning system at a speed which circulates air within a building at a rate that is commensurate with demand under the then-existing conditions.